Background: Estimating sarcopenia by measuring psoas muscle density (PMD) has been advocated as a method to accurately predict post-operative morbidity. The aim of the present study was to determine whether the Timed Stair Climb (TSC) could be used to replace PMD measurements in predicting morbidity. Methods: Patients were prospectively enrolled from March 2014–2015 and were eligible if they were undergoing an abdominal operation. PMD was measured using pre-operative CT scans obtained within 90 days of surgery. Ninety-day complications were assessed using the Accordion Severity Grading System. Multivariable analysis was performed to identify risk factors associated with operative morbidity. Results: Of the patients, 298 were enrolled and completed TSC prior to undergoing an operation. Using the According Grading System, a grade 2 or higher complication occurred in 72 (24. 2%) patients with 8 (2.7%) deaths. There was an indirect relationship between PMD and TSC (P < 0.0001) and a direct relationship between TSC and complications (P = 0.04). On multivariable analysis decreasing PMD (P = 0.018) and increasing TSC (P = 0.026) were predictive of post-operative morbidity. Receiver operating characteristic curves demonstrated that the TSC was superior to both the ACS NSQIP Risk Calculator and PMD in predicting outcomes (TSC vs. PMD, P = 0.012; PMD vs. ACS NSQIP, P = 0.013; TSC vs. ACS NSQIP, P < 0.0001). Conclusion: TSC, PMD, and the ACS NSQIP calculator are all useful tools; however, the TSC is superior in predicting post-operative morbidity.